The Lawrence Livermore National Laboratory tries to answer those questions each year in the form of a "flow" diagram. On the left side of the diagram are the different forms of energy that are produced in or imported to the U.S. and on the right are the eventual uses to which this energy is put. On the top left the yellow bar represents the solar energy produced in 2013. At the bottom left the wide green bar represents petroleum products that were used as energy. The left side bars go from the least carbon intensive energy forms (solar, nuclear, hydro) down to the most carbon intense forms of energy (coal, biomass, petroleum).

This is a Sankey diagram in which the size of the pipes or "spaghetti noodles" indicate the relative amounts of energy flowing. Petroleum was by far the largest energy source in 2013 as well as the most polluting.

On the right side of the diagram are four pink boxes which are the four final uses to which energy is put in the U.S. economy. One way to think about it is that most energy is used in buildings (the three top pink boxes) - factories, homes, places of business - and the second way energy is used is for transportation (the bottom pink box). Trucks, cars, marine vessels, trains, airplanes use a great deal of energy and most of it is in the form of liquid fuels such as diesel, gasoline, aviation fuel, kerosene and other petroleum products.

There is also a light grey image in the background called "rejected energy". This is the energy that is generated and distributed but never gets put to good use. It is energy that is lost on transmission lines, that is wasted in inefficient cars and homes that are poorly built. It is energy that was used to produce, transport and cook food that was thrown away.

Not all energy can be used under current technologies but energy efficient homes, factories and cars can go a long way to reducing waste. All of the costs, including environmental damage that goes into producing energy, is avoided with efficient processes.

This diagram is a snapshot of the U.S. energy flow in 2013. The flows have been changing over time. For example coal use has probably peaked and is now likely to get smaller each year. Solar and wind are growing. This diagram would look very different if it were made for other countries. France gets most of its electricity from nuclear power plants, for example, and Denmark has a great deal of wind power.

China uses a great deal of coal to fuel its economy which causes both health hazards and political protest. The article linked below shows how China is shifting its energy forms - and also how inefficient its energy system is in meeting the needs of its society.

You are a bundle of energy – literally. The number you see when you step on a scale is a measure of the energy that is stored in your body as fat, muscle, bones and the rest of the biological you. At some level most of us understand that the amount of food we eat in the form of calories has to equal the amount of energy we expend or the scale moves up or down. We gain weight if we eat and drink too much energy in the form of calories – a calorie is a measure of thermal (heat) energy needed to raise the temperature of a gram of water by I degree Celsius. If our energy intake is less than what we need to fuel our bodies, then we lose stored energy and that is measured as weight loss.

Anyone who has ever been on a weight loss/gain diet is well aware of the caloric value of popular foods. Carbohydrates and proteins contain 4 calories per gram, while energy-dense fat contains 9 calories. Fats even taste rich.

That’s basic thermo biology. But what do food calories have to do with the social issues surrounding energy?

Plenty.

Calories are fuel for work. In the post-industrial world we use the term “work” to mean a job such as being a taxi driver or the mental activity in an occupation such as accounting. But work has an earlier meaning as the physical labor in farming, hunting and the other activities needed to produce the means of human subsistence.

Until the industrial revolution and the application of inanimate machines to production, human and animal labor were the primary sources of work. (Physicists use work to refer similarly to energy acting as a force on, for example, an object).

So food is the primary fuel for human physical subsistence. It enables us to create shelter and clothing, raise our young, and search for more nutrients.

Those of us in affluent societies may not spend time searching for food because it is available seemingly everywhere - if we can afford it. It comes from the large cornucopias we call supermarkets, vending machines, even the local gasoline station where we can fuel our vehicles and ourselves at the same time. Time-intensive food search and preparation may indicate the presence of a foodie, not scarcity.

Modern humans - Homo sapiens sapiens - have notably big heads - with large brains inside. When lined up next to chimpanzees, gorillas, baboons and other primates humans have proportionally larger skulls and brains, and smaller rib cages and jaws. Compared to other primates and mammals, humans and our earlier hominid ancestors devote less body space and energy to digesting food - and far more to energetically supporting our big brains. This is called “encephalization” by primatologists, that is we have relatively large brain mass relative to our body mass.

Why and how did we evolve in this way? Although the science isn't settled there are intriguing theories and they involvefood as fuel for those big brains.

Homo heidelbergensis reconstruction - Wikipedia

Humans and our hominin bipedal ancestors such as Homo heidelbergensis and Homo neanderthalensis have been transforming the natural environment in order to more efficiently seize and process nutrients for millennia.

According to some anthropologists humans could develop intellectually (and therefore become more socially and culturally complex) by shifting energy away from our guts and toward our brains. The “expensive-tissue hypothesis” is the idea that big brains are energetically demanding tissues and in order to support them food has to be easily digested. Brains demand quality glucose as fuel. Glucose is the only fuel that our brains use.

Humans cannot eat cellulosically dense grasses, as do ruminants and other big-gut animals whose digestive systems expend energy to break down bulk. Rather humans eat easily digested grains, seeds and nuts and meats. Further, milling, crushing, cooking and fermentation and other preparation processes unlock nutrients before eating and aid digestion. So our refined-fuel diets and our intellectual capacity are directly connected according to this hypothesis. We use tools and fire to harvest and process food. Over time we evolved small teeth and slimmer bodies because we didn't need big digestive factories like cows and gorillas because we start to process our food outside of our bodies.

The earliest use of stone tools is traced to Homo habilis some 2.8 million years ago. Homo erectus and Homo ergaster were the first hominids to leave Africa and are believed to be the first to use fire and complex tools. Capturing energy by using our brains has been going on a long time.

References and additional reading:

Aiello, Leslie C., and Peter Wheeler. 1995. “The Expensive-tissue Hypothesis: The Brain and the Digestive System in Human and Primate Evolution”. Current Anthropology 36 (2). [University of Chicago Press, Wenner-Gren Foundation for Ant

Benjamin Franklin proved that electricity and lightening are the same thing using a kite, silk, and a string in the 1750s. He invented the lightning rod so that lightning bolts would hit the rod and not the house - and burn it down. In the years since then electricity has been produced and distributed under controlled circumstances to many regions.Image courtesy of noaa.gov

Does electricity have a social life? We learn in science class that electricity is a physical property that we ascribe to the movement or potential of subatomic particles. We call electrons that flow through wires and other conductive materials an electric current. For most of us we think about electricity for what it does – enables us to light our homes, run big turbines and televisions or in other ways performs useful work.

Can electricity be understood in social as well as physical terms?

I’d like to suggest that it can and I’m going to use the Systems of Exchange typology to make this argument.

The Systems of Exchange typology describes exchange behaviors as motivated by different forms of social relations and different ways of being rational. People can treat everyone the same (universalistic) or some people differently (particularistic), such as friends and family. People may be rational in two fundamentally different ways. They can be instrumentally rational and evaluate the economic efficiency of their choices (e.g. getting the best price), or they can be substantively rational and evaluate choices based on how well it helps to achieve or reflect a value (e.g. which is most fair, or honorable).

The four types that flow from these dimensions are represented as logical systems that are qualitatively different. They are social worlds that orient decisions an action in predictable ways. A price system approximates an auction market, and a communal system would describe a family business where family values and relations make a difference in how the firm works. The SOE website has many cases that illustrate these differences.

Systems of Exchange

THE SYSTEMS OF EXCHANGE TYPOLOGY is described further at http://systemsofexchange.org

Let’s see what happens when we treat electricity as a resource that can be subject to social processes and meanings.

Although electricity is very much a physical phenomenon it is also a social phenomenon in a number of ways. In this instance we can intuit that electrical resources have very different meanings depending who and where you are located socially.

Electricity can have multiple social meanings and be allocated according to very different principles depending on how meanings are applied to it.

In a price system, such as large regional markets that balance electrical loads over multiple utilities price plays a large role. Enron, the now discredited and bankrupt energy company, manipulated the electricity market seeking an advantage. Until reforms caused by the collapse of the large Pacific Gas and Electricity Company due to this market manipulation, price and demand played huge roles in allocation. The growth of community solar aggregation is an example of people coming together to collectively establish a solar electricity resource. They find gains and efficiency by bundling their demand and having greater buying power and lower maintenance costs for solar panels.

The use of lifeline rates by utilities to provide humanitarian energy assistance to low income customers is an example of how values can shape what is considered an inviolable right to heating, cooling and other electrical services. During the Great Recession some utilities extended lifeline rates to as many as 30% of their customers.

How can this analysis be useful? First it helps us to recognize the social in apparently natural phenomena. People have different ways of interpreting the fundamental nature of what are basically electrons. The way they are packaged and distributed and priced is shaped by social beliefs and institutions.

Secondly, if we recognize these differences we can fashion better energy policies that take into account the public’s understandings. Price may be an important allocation principle, but it is not the only one.

American Gothic, 1930 by Grant Wood. Courtesy of the Art Institute of Chicago.

I think many people think about farming as “old technology”. Many of us have mental images of farmers that look like the Midwesterners in Grant Wood’s iconic painting, American Gothic.

However, looked at over the duration of human existence agriculture was a revolutionary moment and farmers were revolutionaries.

Imagine yourself as one of the early modern humans who emerged from east Africa some 100,000 to 400,000 years ago. You were part of a small society among similar others that spread out to the eastern Mediterranean and Middle East Europe and eventually to China and elsewhere.

As a member of a small hunter-gatherer society you spent much of your day looking for food and water. Early people had a number of strategies for provisioning themselves depending on where they were located. Their physical environment – whether they were in woodlands or grasslands, on mountains or in coastal areas – shaped what resources were available and how they could serve as energy sources – calories and materials for heat and cooking.

Hunter-gatherers often had deep knowledge of a region’s edible plants and animals and had diverse diets. Nomadic people traveled to follow available food sources as they were exhausted by periodic overconsumption or made more available over changing seasons.

Agriculture probably emerged as a strategy for providing food energy between 13,000 and 11,000 years ago. Archeologists think that the earliest farming settlements were in the “Fertile Crescent” of Mesopotamia where domesticated grains including wheat and barley were cultivated. Independently, rice cultivation developed in the Ganges Valley of India and the Yangzi Valley of China where different wild grasses became food staples.

There were other regions where hunting wild animals turned into a form of herd management in order to reduce the effort of finding animals. In some jungle environments, such as the New Guinea highlands, forests were manipulated to favor crops of bananas, taro and other nutrient-dense foods. Humans manipulated their environments to produce food energy.

Domesticating seeds, animals, and cultivating land enabled fewer people to provide food energy for the group, and it took fewer hours in the day. Agricultural technologies made farming even more efficient and food preservation technologies enabled people to stockpile food. Given growing food security Neolithic populations developed into villages and new cultural practices emerged to manage relations among larger settled groups.

When farming began the Earth supported about 4 million people. But the ready supply of food energy supported the growth of humans as a species. By the beginning of the industrial revolution there were more than 700 million people. Today the Earth supports more than 7.5 billion people, many through industrial agriculture. Industrial agriculture is aided by the energy revolution that spurred on the Industrial Revolution, but the first energy revolution was farming.

We know that food gives us energy to work, play and live our lives. We also know that food produces energy and that all foods can be measured for its energy content which we express as calories, kilocalories (Kcals), or joules.

But did you know that the reverse is true, that energy produces food? Yes, when you look at what it takes to produce food, whether it is a head of lettuce or a big steak you can express the inputs that were necessary to produce that meal as energy.

It takes food to produce human energy and it takes energy to produce food.

Let's dig a little deeper.

Growing foods such as wheat, apples, and chickens requires energy to produce and then to move from the farm to your plate. Depending on the food you choose there might be fertilizers, water delivery, pesticides, energy for farm machinery and processes such as canning, freezing, packaging and transportation. Each step of the way is part of the life cycle – from farm to fork.

Scientists can measure the energy needed to complete the lifecycle but in fact it is only the energy that produces greenhouse gases (GHGs) that typically are concerned in a lifecycle analysis (LCA). Solar energy from the sun for example does not contribute to climate change, nor does the wind- or water power that drives a grain mill. But the energy needed to produce fertilizers such as nitrous oxide or diesel pumps used for irrigation contributes GHGs and have environmental impacts.

If you buy food at your local farmer’s market it probably does not have packaging and has not traveled far, so it will have a lower carbon footprint from frozen or canned foods traveling from abroad. The same is true for organic foods that do not use industrial fertilizers.

The amount of GHGs used to produce our food is substantial, as much as 30% of all emissions. But not all choices are equally GHG-intensive.

If you live in the UK and drink four cups of black tea a day boiling only the water you need over a year you will use 30kg of CO2. That’s what it would take to drive a typical car 40 miles.

But if you drink 3 large lattes a day you will use enough energy to fly halfway across Europe. Why the difference? It’s all in the milk. Ruminant cows belch a lot of methane while chewing their cuds to digest grass. Methane is an especially damaging greenhouse gas.

If you are interested in the carbon footprint of the foods you eat take a look at Mike Berners-Lee’s book How Bad are Bananas? The Carbon Footprint of Everything. I believe you’ll stop buying out-of-season air-freighted asparagus.

The Hoover Dam (formerly Boulder Dam) was constructed between 1931 and 1936 during the Great Depression. When built the dam was the largest in the world and understood to be a major engineering accomplishment.

The dam was built to control water from the Colorado River to produce electricity and reduce flooding, but especially to assist agriculture in the arid southwest. Lake Mead was formed by the dam and is a tourist attraction that supports boaters and sightseers when the lake is full.

As anticipated housing and agriculture increased dramatically along the path of the newly controlled river. The environmental ramifications of Colorado River control were unforeseen however and species dependent on periodic flooding have been damaged. Lake Mead is now at very low levels given years of drought, and an increasingly arid West appears to be the new normal under conditions of climate change. Disputes over the reduced flow of water and electricity between seven boundary states and Mexico are continuous and are not likely to be resolved in the foreseeable future..

Today we understand Hoover Dam to be the technical marvel it was intended to be, but we also understand more about the context - social and environmental - in which it was built.

For example this extraordinary project was very much a collaboration between a national government and the engineering profession. US President Herbert Hoover, an internationally known professional engineer, worked hard to get financial and political support for the project.

Engineers are trained to be technical experts and to solve complex issues using physics, chemistry, mathematics and other scientific approaches to defining problems and solutions. Engineers are taught to have scientifically rational approaches to projects. The Hoover Dam is a monument to engineering capability as it existed in the 1930s.

However, in retrospect we can see that the Dam did not incorporate a more holistic and social approach to the construction. Native populations, human and animal, were given little consideration and there was insufficient anticipation of the impact of future population growth and climate change on the environment and the population as it grew.

Socio-technical approaches to technology development and introduction consider the larger social and environmental context and try to jointly optimize solutions. Rather than maximize solutions on a technical or social or environmental dimension solutions that balance considerations among the three dimensions are more likely to be flexible in the face of changing circumstances.